7683	2012-08-19 10:09:22	Ashhar Farhan	brass permeability at vhf
Message	Date	From	Subject
i have run out of trimmers. i was thinking of tuning VHF bandpass filters with coils made of silver wire wound over teflon former with a tap for the standard brass M3 screws. is there any literature on brass coils at VHF? - farhan ps, i have ordered this : until this http://www.ebay.com/itm/CV31D-350-CV31D-TUSONIC-CERAMIC-TRIMMER-CAPACITOR-9-35PF-200V-PC-MOUNT-BX4-/251127519819?pt=Vintage_Electronics_R2&hash=item3a785dda4b [Non-text portions of this message have been removed]
7684	2012-08-19 10:24:39	Paul Daulton	Re: brass permeability at vhf
I googled "brasss permability at vhf" and came up with several hits. See http://en.wikipedia.org/wiki/Skin_effect Paul k5wms Quoting Ashhar Farhan : i have run out of trimmers. i was thinking of tuning VHF bandpass filters with coils made of silver wire wound over teflon former with a tap for the standard brass M3 screws. is there any literature on brass coils at VHF? - farhan ps, i have ordered this : until this http://www.ebay.com/itm/CV31D-350-CV31D-TUSONIC-CERAMIC-TRIMMER-CAPACITOR-9-35PF-200V-PC-MOUNT-BX4-/251127519819?pt=Vintage_Electronics_R2&hash=item3a785dda4b [Non-text portions of this message have been removed] Paul Daulton K5WMS beacon WMS 185.302 khz qrss30/slow 24/7 Jacksonville,Ar 72076 em34wu [Non-text portions of this message have been removed]
7685	2012-08-19 11:29:51	KK7B	Re: brass permeability at vhf
Hi Farhan, I have measured an unloaded Q of just over 1000 for a 1/4" 20 brass bolt used as the center conductor of a copper pipe coaxial resonator at 1.3 GHz. Replacing the bolt with an exact replacement in stainless steel reduced the unloaded Q to just under 300. I did not have an opportunity to measure copper or silver plated brass. There are a number of different alloys of brass. I encourage experiments and careful measurements, but I expect that brass screws will be a good choice in your application. Note that ketchup, a comm
7686	2012-08-19 12:14:25	Paul Anderson	Re: brass permeability at vhf
Another way to go for cleaning metal surfaces is to take a slice of lemon, put salt on it, then rub that on the part. It's something that used to be used by jewelers for pickling small soldered joints. One of my favourite tricks when having dinner out is to use that to clean the tarnish off a penny. -----
7687	2012-08-19 12:22:22	Paul Daulton	Re: brass permeability at vhf
Rick thanks for the heads up on ketchup for cleanng brass and copper. I remember back in the '60s International xtal used trimmers made from plastic tubes with a brass screw and a brass sleeve in their tube type vhf converters. The base of the trimmer was metal with lugs, the base snapped in a hole and one soldered the tabs to the circuit board. For a slug tuned coil brass raises the freq where iron or ferrite lowers the freq like some brass screw tuned vfo's , correct? Paul k5wms Quoting KK7B : Hi Farhan, I have measured an unloaded Q of just over 1000 for a 1/4" 20 brass bolt used as the center conductor of a copper pipe coaxial resonator at 1.3 GHz. Replacing the bolt with an exact replacement in stainless steel reduced the unloaded Q to just under 300. I did not have an opportunity to measure copper or silver plated brass. There are a number of different alloys of brass. I encourage experiments and careful measurements, but I expect that brass screws will be a good choice in your application. Note that ketchup, a comm
7688	2012-08-19 12:39:11	Ashhar Farhan	Re: brass permeability at vhf
rick, paul and paul, thanks for all the inputs. i wish i had the gear that i am building now to measure the Q. it is essentially a sweeper + power meter. the sweeper is an Si570. all controlled and measured by an arduino. however, i suppose i can still measure the Q at 144 MHz, using my FT-817 as a signal generator. let me make some measurements. yes, i do have 1/4 inch, 20 tpi brass bolts. - farhan